2.1: Individuals, Species, Populations, Communities And Ecosystems Flashcards
Example of J-cuve: bison
1800: hunters decimate population of American Plains Bison
1889: around 1000 left in wild
US gov + private landowners: established protected herds in late 1800s - early 1900s
Herds started small -> plentiful resources + few predators = population grew quickly
Bison population in northern Yellowstone:
21 in 1902 to 250 in 1915
Example of J-cuve: cane toad
Invasive species: species is introduced to an ecosystem + outcompete native species -> population can grow exponentially
Toad introduced in Australia -> control agricultural crop pests on sugar cane
- invasive species -> reproduced heavily
- toxic secretion -> skin threat to other animals/predators/humans
Australian instructed to kill them
Example of J-cuve: humans
Our population exploded -> ultimately reach limit -> negative feedback mechanism
Evidence of long term sustainability
Some ecosystems: persisted for millions of years -> long term resilience and sustainability
Ex: tropical rainforests
- despite changes in climate + other external factors -> ecosystem endured
Amazon rainforest:
Remain stable despite external pressures (ex: deforestation)
High biodiversity
Complex interactions
= resilience
Human impact on on ecosystem stability: deforestation in that Amazon Rainforests (1)
Deforestation: clearing of trees for agriculture, logging or urban development
- reduces generation of water vapor (via plant through transpiration)
Impact on climate:
Reduced transpiration -> decrease in amount of water vapor in local atmosphere
Water vapor essential -> cloud formation, precipitation (+ cooling effect), maintaining regional climate patterns
-> deforestation disrupt local and regional climate systems
Human impact on on ecosystem stability: deforestation in that Amazon Rainforests (2)
Feed-back loop:
Deforestation -> positive feedback loop
Reduced precipitation -> forest more susceptible to drought/wildfires -> accelerated deforestation -> less transpiration + water vapor for precipitation
New equilibrium:
Deforestation continues at current rate -> not long till amazon rainforest reaches new equilibrium
New equilibrium -> different species, reduced biodiversity, different climate patterns
Keystone species: sea otters
Found in Pacific Northwest in kelp forests
- California -> Alaska
Robert Paine + James estes
- idea to remove otters and test impact
- used estes knowledge of otters (sea otter physiology)
- compare ecosystem with/without sea otters
- amachika -> sea urchins common but small
- shemya -> no kelp all urchin -> loss of otter change entire ecosystem
Regulate population of sea urchins in pacific kelp forests
Sea urchins -> feed on kelp
Without otters -> population explode
Without sea otter -> urchin barren
- sea urchins overgraze kelp -> destroy kelp forest community
Keystone species: purple sea stars
First species identified as a keystone species
Study conducted by Robert Paine (1963)
- identify all organisms in food web -> purple starfish apex
- wonder what would happen if no starfish -> threw into ocean
- collect info
- top predator removed -> number of species from 15 to 8
- line of mussel wen down the rock face -> pushed other species out
Control mussel populations -> otherwise dominate and outcompete rest of species
Allow biodiversity to be maintained
Keystone species: African elephants
Feed on shrubs and trees
- prevent from becoming too dense/dominating landscapes
Browsing behavior -> gaps in vegetation
- promote growth of grasses, increase habitat diversity
- habitat for great variety of species -> increased species diversity
Movement + feeding activities -> contribute to soil nutrient cycling
- redistribute nutrients
- increase soil fertility + plant growth
Human impact on biosphere integrity: evidence from extinction rates
Extinction rates: tangible evidence that planetary boundary for biosphere integrity has been crossed
Highly accelerated rates of species extinction in recent times
- severe disturbance to ecosystems + loss of biodiversity
Human induced factors like:
- habitat destruction
- pollution
- climate change
Drive extinction rates to unprecedented levels
Human impact on biosphere integrity: avoiding critical tipping points
Reversing is crucial to prevent large shifts in earths ecosystems:
- address ecosystem damage + species loss -> essential to avoid tipping point
- ecosystem conservation effort -> preserve structure, function, diversity of ecosystem
- protecting ecosystem -> slow rate of damage, reduce risk of irreversible damage
Preserving species also key factor:
- each species -> unique ecological niche -> contribute to stability + resilience
- protect ecosystem -> preserve niche requirements -> essential for ongoing survival of individuals species
Strategies to protect ecosystem/preserve species diversity:
- Habitat conservation: protect natural habitat from destruction/fragmentation
- species conservation: specific methods to protect most endangered species
- sustainable resource management: promoting sustainable practices + ensure responsible use of natural resources w/o degrading ecosystem
